I'm running Slackware15 on an MSI model: MS-16R5
I'm using a
HP 5-button Optical Comfort Mouse Mice (BR376AA)
lsusb shows
Bus 001 Device 002: ID 0461:4de3 Primax Electronics, Ltd HP 5-Button Optical Comfort Mouse
the mouse works fine
what I found by trial and error is
the two extra side buttons do a page forward and page back on firefox. seamonkey, chrome (alt left arrow) , alt right arrow )
the wheel works fine on many applications like the above plus kate , leafpad ...
the button on the wheel (push the wheel sideways ) doesn't seem to do anything.
how do I change what the extra buttons do ?
on windows hp has something called HP Accessory Center (HPAC) that I think does this.

bash-5.1$ xinput list 11
Primax USB OPTICAL MOUSE id=11 [slave pointer (2)]
Reporting 7 classes:
Class originated from: 11. Type: XIButtonClass
Buttons supported: 9
Button labels: "Button Left" "Button Middle" "Button Right" "Button Wheel Up" "Button Wheel Down" "Button Horiz Wheel Left" "Button Horiz Wheel Right" "Button Side" "Button Extra"
Button state:
Class originated from: 11. Type: XIValuatorClass
Detail for Valuator 0:
Label: Rel X
Range: -1.000000 - -1.000000
Resolution: 0 units/m
Mode: relative
Class originated from: 11. Type: XIValuatorClass
Detail for Valuator 1:
Label: Rel Y
Range: -1.000000 - -1.000000
Resolution: 0 units/m
Mode: relative
Class originated from: 11. Type: XIValuatorClass
Detail for Valuator 2:
Label: Rel Horiz Scroll
Range: -1.000000 - -1.000000
Resolution: 0 units/m
Mode: relative
Class originated from: 11. Type: XIValuatorClass
Detail for Valuator 3:
Label: Rel Vert Scroll
Range: -1.000000 - -1.000000
Resolution: 0 units/m
Mode: relative
Class originated from: 11. Type: XIScrollClass
Scroll info for Valuator 2
type: 2 (horizontal)
increment: 120.000000
flags: 0x0
Class originated from: 11. Type: XIScrollClass
Scroll info for Valuator 3
type: 1 (vertical)
increment: 120.000000
flags: 0x0

bash-5.1$

This is how the whole thing looks in CODE tags. Makes a difference, wouldn't you say? So please take my (and others!) request to heart.

So, 9 buttons are available. You should be able to do with them whatever you want - but things start getting confusing now:

• remapping buttons to other buttons should be possible with xinput, under both Xorg and wayland
• more advanced stuff sometimes depends on whether you're using Xorg or wayland - here are two links:
  https://wiki.archlinux.org/title/Mouse_buttons
  https://medevel.com/configure-extra-...linux-manjaro/

A web search for linux change extra mouse button behavior or some such should get you more suggestions.

Thanks
so its really a 9 button mouse